
ET 200S in the PROFIBUS Network
4-10
ET 200S IM 151-7 CPU Interface Module
A5E00058783-04
Force test function
In the case of the IM 151-7 CPU, you can preset the inputs and the outputs in the
process image with fixed values using the ”Force” function.
The values (force values) you have preset can still be controlled in the
IM 151-7 CPU by the user program and by PD/OP functions. This is shown in
Figure 4-6.
You can force a maximum of 10 variables with the IM 151-7 CPU.
!
Caution
The force values in the process-image input table can be overwritten by write
commands (for example T IB x, = I x.y, copy with SFC, etc.) as well as by I/O read
commands (L PIW x, for example) in the user program or by PD/OP write
functions.
Outputs preset with force values only return the force value provided the user
program does not execute any write accesses to the outputs using I/O write
commands (e.g. T PQB x) and provided no PD/OP functions write to these
outputs.
It is important to note that force values in the process-image input/output table
cannot be overwritten by the user program or by PD/OP functions.
Principle behind forcing with the IM 151-7 CPU
Execute force
job for outputs
PII
transfer
User program
OS
T PQW
Forced value
overwritten by T
PQW!
Execute force
job for inputs
Forced value
Execute force
job for outputs
Forced value
Execute force
job for inputs
OS .... Operating system execution
PIQ
transfer
PII
transfer
OS
PIQ
transfer
Figure 4-6 Principle behind forcing
Comentarios a estos manuales